This thesis attempts to show that an adequate account of human agency requires postulation of a substantial self that is intrinsically active. It proposes and defends a coherent picture of this self's relation to its states, notably, to its motives; and it tries to establish the conditions for freedom-qua-autonomy.It is first shown that the "action-event" distinction is real and ontologically significant. Explanations of this distinction are found to come in two types: event-causal and agent-causal. Each, in turn, is examined.Event-causal accounts fall into two sorts: one sort I call theories; the other I term analyses. Theories are event-causal accounts that treat the active element in action to be irreducible and unanalyzable. They locate this element in some event-type, like the volition. (O'Shaughnessy's view is the main example investigated here). Analyses, in contrast, are attempts to show that action is merely a complex of non-active events causally related in a suitable manner (Goldman's and Davidson's views are investigated here). Both event-causal types of accounts of action are shown to be inadequate.In light of the flaws of event-causal accounts, various alternative agent-causal theories (e.g., Chisholm's, Sartre's) are explored. Using the results of this study, a comprehensive agent-causal theory is developed and defended. This theory postulates an intrinsically active substantial self as the agent--as oneself. Defense of this notion rests in part upon a unique experiential phenomenon: that of continuous sustained causation of a lasting process. Objections to this type of theory (notably, Thalberg's and Davidson's) are then addressed. There follows an account of how the self is related to its states in general, and to its motives (that is, desires, principles, etc.) in particular.The final chapter is devoted to freedom-qua-autonomy. It is argued that activeness is only a necessary condition for autonomy. A further requirement is the agent-self's 'appropriation' of the motives operative in an act. Appropriation of a motive is construed as resulting from the agent's active, reflexive participation in the motive's emergence and/or continued existence.